As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. Among them is a lithium secondary battery having high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
Based on their external and internal structures, secondary batteries are generally classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery. Especially, the prismatic battery and the pouch-shaped battery, which can be stacked with high integration and have a small width to length ratio, have attracted considerable attention.
Also, the secondary batteries have attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, kinds of applications using the secondary batteries are being increased owing to advantages of the secondary batteries, and hereafter the secondary batteries are expected to be applied to more applications and products than now.
As kinds of applications and products, to which the secondary batteries are applicable, are increased, kinds of batteries are also increased such that the batteries can provide powers and capacities corresponding to the various applications and products. Furthermore, there is a strong need to reduce the sizes and weights of the batteries applied to the corresponding applications and products.
For example, small-sized mobile devices, such as mobile phones, personal digital assistants (PDA), digital cameras, and laptop computers, use one or several small-sized, light-weighted battery cells for each device according to the reduction in size and weight of the corresponding products. On the other hand, middle- or large-sized devices, such as electric vehicles and hybrid electric vehicles, use a middle- or large-sized battery module (which may be referred to as “a battery pack”) having a plurality of battery cells electrically connected with each other because high power and large capacity is necessary for the middle- or large-sized devices. The size and weight of the battery module is directly related to the receiving space and power of the corresponding middle- or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, light-weighted battery modules.
Meanwhile, as battery cells are connected to one another, while the battery cells are stacked, to increase the capacities of battery modules, the dissipation of heat from the battery cells becomes serious. Heat is generated from lithium secondary batteries during the charge and discharge of the lithium secondary batteries. If the heat is not effectively removed, the heat accumulates in the respective lithium secondary batteries, with the result that the deterioration of the secondary batteries is caused, and the safety of the secondary batteries is greatly lowered. In particular, for a battery requiring high-speed charging and discharging characteristics as in a power source for electric vehicles and hybrid electric vehicles, a large amount of heat is generated from the battery at the time when the battery instantaneously provides high power.
Also, a laminate type battery case of a pouch-shaped battery cell widely used in the battery module is coated with a polymer material exhibiting low heat conductivity, with the result that it is difficult to effectively lower the overall temperature of the battery.
In connection with this matter, for example, Korean Patent Application Publication No. 2006-0034130 discloses a sheathing member for batteries including a metal plate having a first surface which is approximately flat and a second surface which is approximately flat, the second surface being opposite to the first surface, a heat dissipation layer formed on the first surface of the metal plate to a predetermined thickness, and a cast propylene (CPP) layer formed on the second surface of the metal plate to a predetermined thickness. That is, the disclosed sheathing member for batteries is constructed in a structure in which the CPP layer, the metal layer, and the heat dissipation layer are sequentially stacked from the inside of a battery. Consequently, an outer resin layer exhibiting excellent durability is substantially removed from the outer surface of a laminate-type battery case, with the result that the durability of the battery case may be lowered. In addition, an additional process for coating the heat dissipation layer is required, which complicates the manufacturing process.
Therefore, there is a high necessity for a technology that is capable of fundamentally solving the above-mentioned problems.